Communication devices, such as portable radio telephones, which offer duplex communications often suffer from an acoustic feedback problem commonly referred to as echo. Echo generally occurs when audio sourced at a first communication unit is received by a second communication unit which audio is then retransmitted by the second communication unit to the first communication unit after an appreciable amount of delay. One of the most effective ways to suppress echo is to decouple the audio received and outputted at a particular communication device from the audio transmitted by that device. The prior art describes a variety of mechanical, electrical, and software solutions which attempt to adequately address this issue. Many practical implementations involve a combination of mechanical design and signal processing in an attempt to suppress the effects of echo.
FIG. 1 shows one prior art approach for an echo canceller 100 where signal processing is used to account for the presence of echo resulting from the coupling of an audio output signal 102 into an audio input signal 104. Here, the audio output signal 102 is sampled and used by a least mean squared (LMS) error adaptive filter 106 to remove echo energy from the audio input signal. The resultant filtered signal 108 substitutes for the original audio input signal 104, as it is expected to be superior to the original audio input signal 104.
One problem with this prior art implementation is that the LMS algorithm used can occasionally produce a worse signal by amplifying echo or by amplifying noise. This may occur when the echo canceller adapts its filter using noisy audio output signals or when the echo canceller attempts to filter an input signal which is uncorrelated with the audio output signal. Thus, the resultant filtered signal may be inferior to that of the original signal.
It is desirable to provide an echo cancellation technique which overcomes the problems discussed with respect to the prior art. Preferably, a solution should be provided which is not computationally intensive yet which produces significant improvements.